1. Field of the Invention
The invention relates generally to waste disposal method and apparatus, and more particularly to methods and apparatus for effecting disinfection, and optionally sterilization, of waste material such as medical, food and other types of waste, and for reducing the volume of such waste material.
2. Description of the Related Art
Waste management has evolved in the latter part of the twentieth century into an industry of considerable importance, as societal and environmental attention has focused on the conventional processes by which waste has to date been handled for disposal. These conventional waste disposal processes include incineration, dumping at sea, and burial in landfills. Each of these processes, however, is encumbered by significant societal and environmental disadvantages. Incineration is objectionable due to its attendant chemical and particulate pollution of the atmosphere and surrounding locales. Further, these pollutants can be transported over great distances by prevailing winds, thereby extending the scope of environmental impact beyond the immediate locale of the incinerator. Waste disposal in the oceans is objectionable due to its adverse environmental impact on sea life and coastal shores. Landfills are objectionable due to their attendant spatial demands, offensive odors, and potential for production of hazardous substances arising from the mixing and interaction of buried materials. Spatial considerations are especially prevalent in urban centers, where population growth has resulted in suburban expansion to locations well outside of the urban center, necessitating in some instances in the relocation of existing landfills and the creation of costly new landfills at locations geographically remote from the centers they serve.
Additional waste disposal problems arise in view of the type of waste that is to be disposed. For example, special precautions are required for the disposal of biological and medical waste due to the overwhelming concern for preventing the creation and/or spread of infectious disease. Further concerns arise due to the presence of extremely sharp medical instruments such as needles, knives, and broken glass containers that can cut or lacerate the skin of personnel and animals with which the waste comes in contact, thereby presenting both a risk of physical harm and biological contamination. For these reasons, such waste is typically thermally or chemically treated and buried in dedicated medical waste disposal facilities. The treatment can be of a type that results in disinfection, and optimally sterilization, of the waste so as to render it biologically neutral or inert. As used in the description which follows, the term "disinfection" and its variants pertains to the destruction of pathogenic microorganisms or their toxins or vectors, whereas "sterilization" and its variations pertains to the destruction of all living microorganisms and their spores, thereby rendering the material so processed void of all living matter.
Sterilization can typically be accomplished by any one of a variety of prescribed chemical and non-combustion thermal treatment regimens, as well as incineration. Chemical sterilization generally provides for exposure of the waste material to an antiseptic solution such as liquid chlorine for a prescribed time interval; however, the use of chemical sterilizing agents presents disposal problems for the liquid following waste treatment due to the toxicity of chlorine and other antiseptic solutions. A popular alternative to chemical disinfection is autoclaving, which provides for exposure of the waste to heat at upwards of 250.degree. F. (121.degree. C.) at 15 psi for 15-40 minutes. While sterilization can be accomplished in both dry air and steam environments, steam autoclaving is generally preferred due to its greater penetrating capabilities (especially important for sterilizing "soft" waste such as textiles and gauze) and its lethality via the process of denaturation. Longer periods are used to assure steam penetration of heavy, fluid-absorbable loads. Faster processing can be accomplished for some waste materials by increasing temperature and pressure. However, a significant disadvantage of steam autoclaving is its failure to assure complete penetration of the waste and its exposure to the heat contained within the water vapor. Further disadvantages include the tendency for autoclaves (both steam and dry) to stratify and to trap comparatively cool air in pockets, thereby precluding sterilization. In addition, the waste is neither reduced in volume or in mass; instead, mass can increase in some instances (i.e., textiles and gauze) due to the absorption of water vapor, thereby exacerbating the problem of waste disposal referenced above.
In view of the foregoing, there is a pressing societal need to not only reduce the volume of waste material that is produced, but also to more effectively and efficiently process the waste so that it has a diminished environmental impact. The need is especially pressing in instances where waste is produced in bulk, as can occur in hospitals, nursing homes, restaurants and the like. While efforts are being undertaken to reduce waste production, these efforts alone will not eliminate the various problems associated with waste disposal, particularly in the medical and dental industries, where single patient use (i.e., non-reusable) surgical instruments have gained widespread acceptance due to concerns over spread of the family of hepatitis viruses and HIV. Accordingly, the present invention is directed to providing methods and apparatus for disinfecting, and optimally sterilizing, medical and other forms of waste, particularly when such is in bulk form, and reducing the volume of waste solids for disposal. These and other objects and advantages of the present invention will become apparent from the following specification when read in conjunction with the accompanying drawings.